Phosphazene bases: A new category of organocatalysts for the living ring-opening polymerization of cyclic esters

We demonstrate that phosphazene bases, such as 2-te/t-butylimino-2- diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) and N′-tert-butyl-N,N,N′N′,N″,N″- hexamethylphosphorimidic triamide (P1-t-Bu), are active organocatalysts for the living ring-opening polymerization (ROP) of cyclic esters. Polyesters prepared through this organocatalytic route possess predictable molecular weights, narrow polydispersities, and high end-group fidelity. Mechanistic studies suggest that the intermolecular hydrogen bonding of the alcohol initiator to phosphazene bases activates the alcohol for ROP of cyclic esters. © 2007 American Chemical Society.